Gene therapy progress and prospects: cystic fibrosis

Polymeric nano-carriers for on-demand delivery of genes via specific responses to stimuli

Polymeric nano-carriers have been developed as a most capable and feasible technology platform for gene therapy. As vehicles, polymeric nano-carriers are obliged to possess high gene loading capability, low immunogenicity, safety, and the ability to transfer various genetic materials into specific sites of target cells to express therapeutic proteins or block a process of gene expression. To this end, various types of polymeric nano-carriers have been prepared to release genes in response to stimuli such as pH, redox, enzymes, light and temperature. These stimulus-responsive nano-carriers exhibit high gene transfection efficiency and low cytotoxicity. In particular, dual- and multi-stimulus-responsive polymeric nano-carriers can respond to a combination of signals. Markedly, these combined responses take place either simultaneously or in a sequential manner. These dual-stimulus-responsive polymeric nano-carriers can control gene delivery with high gene transfection both in vitro and in vivo. In this review paper, we highlight the recent exciting developments in stimulus-responsive polymeric nano-carriers for gene delivery applications.

The enhancement of osteogenic capacity in a synthetic BMP-2 derived peptide coated mineralized collagen composite in the treatment of the mandibular defects

The novel synthetic peptide P17-BMP-2 could promote cell attachment and enhance osteogenic capability. A composite, comprising nano-hydroxyapatite, collagen and poly(L-lactide) (nHAC/PLLA), was an efficient scaffold for carrier of P17-BMP-2. Our aim was to investigate whether nHAC/PLLA/P17-BMP-2 accelerates the osteogenesis as a reliable method for mandibular defect healing in this study. The repair capability was assessed by the gross observation, X-ray test and histological observation in four animal experiment groups at 2 week and 4 week after surgery: Group A (control), Group B (nHAC/PLLA treatment), Group C (nHAC/PLLA with 2 mg/g P17-BMP-2 treatment) and Group D (nHAC/PLLA with 10 mg/g P17-BMP-2 treatment). The Lane-Sandhu X-ray scores of the four groups were compared among four groups as well. The results showed that the composites containing the highest content of P17- BMP-2 performed best. Therefore, the nHAC/PLLA with P17-BMP-2 composite can accelerate the osteogenesis for mandibular defect healing and could be an ideal biological material as a bone graft material option for clinical applications.

Barriers to inhaled gene therapy of obstructive lung diseases: A review

Knowledge of genetic origins of obstructive lung diseases has made inhaled gene therapy an attractive alternative to the current standards of care that are limited to managing disease symptoms. Initial lung gene therapy clinical trials occurred in the early 1990s following the discovery of the genetic defect responsible for cystic fibrosis (CF), a monogenic disorder. However, despite over two decades of intensive effort, gene therapy has yet to help patients with CF or any other obstructive lung disease. The slow progress is due in part to poor understanding of the biological barriers to inhaled gene therapy. Encouragingly, clinical trials have shown that inhaled gene therapy with various viral vectors and non-viral gene vectors is well tolerated by patients, and continued research has provided valuable lessons and resources that may lead to future success of this therapeutic strategy. In this review, we first introduce representative obstructive lung diseases and examine limitations of currently available therapeutic options. We then review key components for successful execution of inhaled gene therapy, including gene delivery systems, primary physiological barriers and strategies to overcome them, and advances in preclinical disease models with which the most promising systems may be identified for human clinical trials.

Redesign of extensive protein-DNA interfaces of meganucleases using iterative cycles of in vitro compartmentalization

LAGLIDADG homing endonucleases (meganucleases) are sequence-specific DNA cleavage enzymes used for genome engineering. Recently, meganucleases fused to transcription activator-like effectors have been demonstrated to efficiently introduce targeted genome modifications. However, retargeting meganucleases to genomic sequences of interest remains challenging because it usually requires extensive alteration of a large number of amino acid residues that are situated in and near the DNA interface. Here we describe an effective strategy to extensively redesign such an extensive biomolecular interface. Well-characterized meganucleases are computationally screened to identify the best candidate enzyme to target a genomic region; that protein is then redesigned using iterative rounds of in vitro selections within compartmentalized aqueous droplets, which enable screening of extremely large numbers of protein variants at each step. The utility of this approach is illustrated by engineering three different meganucleases to cleave three human genomic sites (found in two exons and one flanking intron in two clinically relevant genes) and a fourth endonuclease that discriminates between single-nucleotide polymorphism variants of one of those targets. Fusion with transcription activator-like effector DNA binding domains significantly enhances targeted modification induced by meganucleases engineered in this study. Simultaneous expression of two such fusion endonucleases results in efficient excision of a defined genomic region.

Emerging drugs for cystic fibrosis

INTRODUCTION

Cystic fibrosis is an autosomal recessive disease, which is the result of a genetic defect in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Pulmonary disease accounts for over 90% of the morbidity and mortality associated with the disease. Conventionally, CF treatment has focused on symptomatic therapy.

AREAS COVERED

In the past, the emphasis for the development of CF therapeutics has previously been on addressing complications of the manifestations rather than on the underlying disease process. However, in the past few decades there has been a paradigm shift with new attention on the underlying biological mechanisms and therapies targeted at curing the disease rather than simply controlling it. This review summarizes the current CF therapeutics pipeline. These developing therapies include CFTR gene therapy, CFTR pharmacotherapeutics, osmotically active agents and anti-inflammatory therapies, as well as novel inhaled antibiotics.

EXPERT OPINION

The CF therapeutics pipeline currently holds great promise both for novel therapies directly targeting the underlying biological mechanisms of CFTR dysfunction and new symptomatic therapies. While CFTR-directed therapy has the highest potential to improve patients' outcome, it is important to continue to develop better treatment options for all aspects of CF lung disease.

Modulation of Treg function improves adenovirus vector-mediated gene expression in the airway

Virus vector-mediated gene transfer has been developed as a treatment for cystic fibrosis (CF) airway disease, a lethal inherited disorder caused by somatic mutations in the cystic fibrosis transmembrane conductance regulator gene. The pathological proinflammatory environment of CF as well as the naïve and adaptive immunity induced by the virus vector itself limits the effectiveness of gene therapy for CF airway. Here, we report the use of an HDAC inhibitor, valproic acid (VPA), to enhance the activity of the regulatory T cells (T(reg)) and to improve the expression of virus vector-mediated gene transfer to the respiratory epithelium. Our study demonstrates the potential utility of VPA, a drug used for over 50 years in humans as an anticonvulsant and mood-stabilizer, in controlling inflammation and improving the efficacy of gene transfer in CF airway.

Lentiviral small hairpin RNA delivery reduces apical sodium channel activity in differentiated human airway epithelial cells

BACKGROUND

Epithelial sodium channel (ENaC) hyperactivity has been implicated in the pathogenesis of cystic fibrosis (CF) by dysregulation of fluid and electrolytes in the airways. In the present study, we show proof-of-principle for ENaC inhibition by lentiviral-mediated RNA interference.

METHODS

Immortalized normal (H441) and CF mutant (CFBE) airway cells, and differentiated human bronchial epithelial cells in air liquid interface culture (HBEC-ALI) were transduced with a vesicular stomatitis virus G glycoprotein pseudotyped lentiviral (LV) vector expressing a short hairpin RNA (shRNA) targeting the α subunit of ENaC (ENaCα), and a marker gene. Efficacy of ENaCα down-regulation was assayed by the real-time polymerase chain reaction (PCR), membrane potential assay, western blotting, short-circuit currents and fluid absorption. Off-target effects were investigated by a lab-on-a-chip quantitative PCR array.

RESULTS

Transduction to near one hundred percentage efficiency of H441, CFBE and HBEC-ALI was achieved by the addition of the LV vector before differentiation and polarization. Transduction resulted in the inhibition of ENaCα mRNA and antigen expression, and a proportional decrease in ENaC-dependent short circuit current and fluid transport. No effect on transepithelial resistance or cAMP-induced secretion responses was observed in HBEC-ALI. The production of interferon α and pro-inflammatory cytokine mRNA, indicating Toll-like receptor 3 or RNA-induced silencing complex mediated off-target effects, was not observed in HBEC-ALI transduced with this vector.

CONCLUSIONS

We have established a generic method for studying the effect of RNA interference in HBEC-ALI using standard lentiviral vectors. Down-regulation of ENaCα by lentiviral shRNA expression vectors as shown in the absence off-target effects has potential therapeutic value in the treatment of cystic fibrosis.

Gene therapy in cystic fibrosis

Cystic fibrosis (CF) is an autosomal recessive disease caused by mutations in the cystic fibrosis transmembrane regulator (CFTR) gene and is the most common life-shortening genetic defect in Caucasians. Life expectancy in CF has improved substantially over the last 75 years because of treatments aimed at end-organ complications. Since the CFTR gene was discovered in 1989 more than 1900 mutations have been reported to cause CF and significant effort has been put forth into gene therapy to find a mutation independent "cure" for CF. Gene-based approaches have not yet led to a viable therapy but have provided insights into hurdles that limit the efficacy of gene therapy. This review will address the nomenclature of CFTR mutations, attempts at viral and nonviral gene therapy, and recent advances in mutation-specific molecules.

In vitro and in vivo enhancement of osteogenic capacity in a synthetic BMP-2 derived peptide-coated mineralized collagen composite

Enhancement of osteogenic capacity was achieved in a mineralized collagen composite, nano-hydroxyapatite/collagen (nHAC), by loading with synthetic peptides derived from BMP-2 residues 32-48 (P17-BMP-2). Rabbit marrow stromal cells (MSCs) were used in vitro to study cell biocompatibility, attachment and differentiation on the mineralized collagen composite by a cell counting kit, scanning electron microscopy (SEM) and real-time reversed transcriptase-polymerase chain reaction analysis (RT-PCR). Optimal peptide dosage (1.0 µg/mL) was obtained by RT-PCR analysis in vitro. In addition, the relative expression level of OPN and OCN was significantly upregulated on P17-BMP-2/nHAC compared with nHAC. In vitro results of P17-BMP-2 release kinetics demonstrated that nHAC released P17-BMP-2 in a controlled and sustained manner. In the rabbit mandibular box-shaped bone defect model, osteogenic capacity of three groups (nHAC, P17-BMP-2/nHAC, rhBMP-2/nHAC) was evaluated. Compared to the nHAC group, bone repair responses in both P17-BMP-2/nHAC and rhBMP-2/nHAC group implants were significantly improved based on histological analysis. The osteogenic response of the P17-BMP-2/nHAC group was similar to that of the rhBMP-2/nHAC group.

Candidate diseases for prenatal gene therapy

Prenatal gene therapy aims to deliver genes to cells and tissues early in prenatal life, allowing correction of a genetic defect, before irreparable tissue damage has occurred. In contrast to postnatal gene therapy, prenatal application may target genes to a large population of stem cells, and the smaller fetal size allows a higher vector to target cell ratio to be achieved. Early gestation delivery may allow the development of immune tolerance to the transgenic protein, which would facilitate postnatal repeat vector administration if needed. Moreover, early delivery would avoid anti-vector immune responses which are often acquired in postnatal life. The NIH Recombinant DNA Advisory Committee considered that a candidate disease for prenatal gene therapy should pose serious morbidity and mortality risks to the fetus or neonate, and not have any effective postnatal treatment. Prenatal gene therapy would therefore be appropriate for life-threatening disorders, in which prenatal gene delivery maintains a clear advantage over cell transplantation or postnatal gene therapy. If deemed safer and more efficacious, prenatal gene therapy may be applicable for nonlethal conditions if adult gene transfer is unlikely to be of benefit. Many candidate diseases will be inherited congenital disorders such as thalassaemia or lysosomal storage disorders. However, obstetric conditions such as fetal growth restriction may also be treated using a targeted gene therapy approach. In each disease, the condition must be diagnosed prenatally, either via antenatal screening and prenatal diagnosis, for example, in the case of hemophilias, or by ultrasound assessment of the fetus, for example, congenital diaphragmatic hernia. In this chapter, we describe some examples of the candidate diseases and discuss how a prenatal gene therapy approach might work.

Personalized medicine in cystic fibrosis: dawning of a new era

Life expectancy in cystic fibrosis (CF) has improved substantially over the last 75 years, with a median predicted survival now approaching 40 years. This improvement has resulted largely from therapies treating end-organ manifestations. In an effort to develop drugs that would target the underlying defects in the CF transmembrane conductance regulator (CFTR), the Cystic Fibrosis Foundation embarked on a bold initiative in which it established collaborations with biopharmaceutical companies to support early-stage efforts to discover new medicines for CF. This has led to the development and clinical trial testing of several novel drugs targeting specific CFTR mutations. One drug, ivacaftor, was recently approved by the US Food and Drug Administration for the approximately 4% of patients with CF who have the G551D gating mutation. Drugs targeting F508del CFTR and premature termination codons, which would be applicable to 90% of patients with CF, are undergoing clinical trials. The impact of such drugs on CFTR biomarkers, such as sweat chloride and nasal potential difference, suggests that they may reset the clinical trajectory of CF, but their effect on long-term outcomes will remain unknown for many years. Nevertheless, development of CFTR-targeted drugs represents an important milestone in CF, perhaps revolutionizing the care of these patients in a fundamental way.

Self-assembled multivalency: dynamic ligand arrays for high-affinity binding

Multivalency is a powerful strategy for achieving high-affinity molecular recognition in biological systems. Recently, attention has begun to focus on using self-assembly rather than covalent scaffold synthesis to organize multiple ligands. This approach has a number of advantages, including ease of synthesis/assembly, tunability of nanostructure morphology and ligands, potential to incorporate multiple active units, and the responsive nature of self-assembly. We suggest that self-assembled multivalency is a strategy of fundamental importance in the design of synthetic nanosystems to intervene in biological pathways and has potential applications in nanomedicine.

A synthetic chloride channel restores chloride conductance in human cystic fibrosis epithelial cells

Mutations in the gene-encoding cystic fibrosis transmembrane conductance regulator (CFTR) cause defective transepithelial transport of chloride (Cl⁻) ions and fluid, thereby becoming responsible for the onset of cystic fibrosis (CF). One strategy to reduce the pathophysiology associated with CF is to increase Cl⁻ transport through alternative pathways. In this paper, we demonstrate that a small synthetic molecule which forms Cl⁻ channels to mediate Cl⁻ transport across lipid bilayer membranes is capable of restoring Cl⁻ permeability in human CF epithelial cells; as a result, it has the potential to become a lead compound for the treatment of human diseases associated with Cl⁻ channel dysfunction.

Controlled pulmonary drug and gene delivery using polymeric nano-carriers

Pulmonary drug and gene delivery to the lung represents a non-invasive avenue for local and systemic therapies. However, the respiratory tract provides substantial barriers that need to be overcome for successful pulmonary application. In this regard, micro- and nano-sized particles offer novel concepts for the development of optimized therapeutic tools in pulmonary research. Polymeric nano-carriers are generally preferred as controlled pulmonary delivery systems due to prolonged retention in the lung. Specific manipulation of nano-carrier characteristics enables the design of "intelligent" carriers specific for modulation of the duration and intensity of pharmacological effects. New formulations should be tested for pulmonary absorption and distribution using more advanced ex vivo and in vivo models. The delivery of nano-carriers to the air-space enables a detailed characterization of the interaction between the carrier vehicle and the natural pulmonary environment. In summary, polymeric nanoparticles seem to be especially promising as controlled delivery systems and represent a solid basis for future advancement for pulmonary delivery applications.

Common gene therapy viral vectors do not efficiently penetrate sputum from cystic fibrosis patients

Norwalk virus and human papilloma virus, two viruses that infect humans at mucosal surfaces, have been found capable of rapidly penetrating human mucus secretions. Viral vectors for gene therapy of Cystic Fibrosis (CF) must similarly penetrate purulent lung airway mucus (sputum) to deliver DNA to airway epithelial cells. However, surprisingly little is known about the rates at which gene delivery vehicles penetrate sputum, including viral vectors used in clinical trials for CF gene therapy. We find that sputum spontaneously expectorated by CF patients efficiently traps two viral vectors commonly used in CF gene therapy trials, adenovirus (d∼80 nm) and adeno-associated virus (AAV serotype 5; d∼20 nm), leading to average effective diffusivities that are ∼3,000-fold and 12,000-fold slower than their theoretical speeds in water, respectively. Both viral vectors are slowed by adhesion, as engineered muco-inert nanoparticles with diameters as large as 200 nm penetrate the same sputum samples at rates only ∼40-fold reduced compared to in pure water. A limited fraction of AAV exhibit sufficiently fast mobility to penetrate physiologically thick sputum layers, likely because of the lower viscous drag and smaller surface area for adhesion to sputum constituents. Nevertheless, poor penetration of CF sputum is likely a major contributor to the ineffectiveness of viral vector based gene therapy in the lungs of CF patients observed to date.

Hydrophobically modified dendrons: developing structure-activity relationships for DNA binding and gene transfection

This paper develops a structure-activity relationship understanding of the way in which surfactant-like dendrons with hydrophilic spermine surface groups and a variety of lipophilic units at their focal points can self-assemble and subsequently bind to DNA with high affinity. The choice of functional group at the focal point of the dendron and the high tunability of the molecular structure have a very significant impact on DNA binding. Mesoscale modeling of the mode of dendron self-assembly provides a direct insight into how the mode of self-assembly exerts its effect on the DNA binding process. In particular, the hydrophobic unit controls the number of dendrons in the self-assembled micellar structures, and hence their diameters and surface charge density. The DNA binding affinity correlates with the surface charge density of the dendron aggregates. Furthermore, these structure-activity effects can also be extended to cellular gene delivery, as surface charge density plays a role in controlling the extent of endosomal escape. It is reported that higher generation dendrons, although binding DNA less strongly than the self-assembling lower generation dendrons, are more effective for transfection. The impact of the lipophilic group at the focal point is less significant for the DNA binding ability of these larger dendrons, which is predominantly controlled by the spermine surface groups, but it does modify the levels of gene transfection. Significant synergistic effects on gene delivery were observed when employing combinations of the dendrons and polyethyleneimine (PEI, 25 kDa), with transfection becoming possible at low loading levels where the two components would not transfect individually, giving practically useful levels of gene delivery.

Emerging therapies in cystic fibrosis

The life expectancy of people with cystic fibrosis (CF), a lethal inherited disease, has been greatly extended by advances in therapy. Currently, there are a number of potential drugs for treatment of CF lung disease in clinical trials. These therapies are targeted at all points in the pathogenesis of lung disease, from gene transfer to drugs that treat mucus, infection and inflammation in the airways. An exciting development is that of modulation of the abnormal protein that causes CF, the cystic fibrosis transmembrane conductance regulator (CFTR), where drugs are targeted at specific defects in CFTR transcription, processing or functioning. Inhaled therapies are being developed to augment airway surface liquid height, either by modulating the abnormal ion channel function in the airway epithelial cell or by rehydrating with osmotic agents. Anti-inflammatory therapy is also of great interest in CF and there are several candidate drugs in clinical trials. A number of antibacterial agents formulated for inhalation are at various stages of study or newly approved, which should improve options for chronic management of airway infection. Hopefully, many of these potential therapies will come to market and will further extend the life expectancy of people with CF.

Stem cell therapy for cystic fibrosis: current status and future prospects

Although cystic fibrosis (CF), an autosomal recessive disease caused by mutations in the gene encoding for the CF transmembrane conductance regulator (CFTR), seems a good candidate for gene therapy, 15 years of intense investigation and a number of clinical trials have not yet produced a viable clinical gene-therapy strategy. In addition, the duration of gene expression has been shown to be limited, only lasting 1-4 weeks. Therefore, alternative approaches involve the search for, and use of, stem cell populations. Bone marrow contains different stem cell types, including hematopoietic stem cells and multipotent mesenchymal stromal cells. Numerous studies have now demonstrated the ability of hematopoietic stem cells and mesenchymal stromal cells to home to the lung and differentiate into epithelial cells of both the conducting airways and the alveolar region. However, engraftment of bone marrow-derived stem cells into the airways is a very inefficient process. Detailed knowledge of the cellular and molecular determinants governing homing to the lung and transformation of marrow cells into lung epithelial cells would benefit this process. Despite a very low level of engraftment of donor cells into the nose and gut, significant CFTR mRNA expression and a measurable level of correction of the electrophysiological defect were observed after transplantation of wild-type marrow cells into CF mice. It is uncertain whether this effect is due to the presence of CFTR-expressing epithelial cells derived from donor cells or to the immunomodulatory role of transplanted cells. Finally, initial studies on the usefulness of umbilical cord blood and embryonic stem cells in the generation of airway epithelial cells will be discussed in this review.

Lysophosphatidylcholine as an adjuvant for lentiviral vector mediated gene transfer to airway epithelium: effect of acyl chain length

BACKGROUND

Poor gene transfer efficiency has been a major problem in developing an effective gene therapy for cystic fibrosis (CF) airway disease. Lysophosphatidylcholine (LPC), a natural airway surfactant, can enhance viral gene transfer in animal models. We examined the electrophysiological and physical effect of airway pre-treatment with variants of LPC on lentiviral (LV) vector gene transfer efficiency in murine nasal airways in vivo.

METHODS

Gene transfer was assessed after 1 week following nasal instillations of a VSV-G pseudotype LV vector pre-treated with a low and high dose of LPC variants. The electrophysiological effects of a range of LPC variants were assessed by nasal transepithelial potential difference measurements (TPD) to determine tight junction permeability. Any physical changes to the epithelium from administration of the LPC variants were noted by histological methods in airway tissue harvested after 1 hour.

RESULTS

Gene transduction was significantly greater compared to control (PBS) for our standard LPC (palmitoyl/stearoyl mixture) treatment and for the majority of the other LPC variants with longer acyl chain lengths. The LPC variant heptadecanoyl also produced significantly greater LV gene transfer compared to our standard LPC mixture. LV gene transfer and the transepithelial depolarization produced by the 0.1% LPC variants at 1 hour were strongly correlated (r2 = 0.94), but at the 1% concentration the correlation was less strong (r2 = 0.59). LPC variants that displayed minor to moderate levels of disruption to the airway epithelium were clearly associated with higher LV gene transfer.

CONCLUSIONS

These findings show the LPC variants effect on airway barrier function and their correlation to the effectiveness of gene expression. The enhanced expression produced by a number of LPC variants should provide new options for preclinical development of efficient airway gene transfer techniques.

Impact of chronic pulmonary infection with Pseudomonas aeruginosa on transfection mediated by viral and nonviral vectors

Pseudomonas aeruginosa plays a crucial role in the lung pathology of cystic fibrosis (CF). We showed that acute infection with P. aeruginosa has a substantial impact on gene transfer into lung epithelial cells mediated by polyplexes. As an extension of those studies we report here on the effect of chronic pulmonary infection with P. aeruginosa on transfection of lung epithelial cells by viral and nonviral vectors. As an in vivo model of the persistent chronic infection in patients with CF we used C57BL/6 mice intratracheally infected with P. aeruginosa encapsulated in agar beads. Two weeks after infection the presence of viable bacteria in the lungs was confirmed, mostly in the bronchial lumen. In lung tissue sections stained with hematoxylin and eosin, extensive inflammatory infiltrations were found. At that time point the mice received an intratracheal dose of luciferase gene complexed with either Lipofectamine (Lf), a GL67 lipid mixture (GL67), or polyethylenimine (PEI) or with lentivirus (LV) as a carrier system. Luciferase activity was determined by a luminescence assay in supernatants of lung homogenates. The transfection level induced by PEI/DNA polyplexes complexed with serum albumin was decreased in infected mice. Lf-mediated transfection was almost completely blocked in infected mice. Transfection levels in mice treated with LV or plain PEI/DNA polyplexes were unchanged in infected animals as compared with control mice. The only carrier that displayed a clearly increased transfection level in infected mice was the GL67 lipid mixture, which is tentatively ascribed to the presence of polyethylene glycol in this carrier.

Toward gene therapy for cystic fibrosis using a lentivirus pseudotyped with Sendai virus envelopes

Gene therapy for cystic fibrosis (CF) is making encouraging progress into clinical trials. However, further improvements in transduction efficiency are desired. To develop a novel gene transfer vector that is improved and truly effective for CF gene therapy, a simian immunodeficiency virus (SIV) was pseudotyped with envelope proteins from Sendai virus (SeV), which is known to efficiently transduce unconditioned airway epithelial cells from the apical side. This novel vector was evaluated in mice in vivo and in vitro directed toward CF gene therapy. Here, we show that (i) we can produce relevant titers of an SIV vector pseudotyped with SeV envelope proteins for in vivo use, (ii) this vector can transduce the respiratory epithelium of the murine nose in vivo at levels that may be relevant for clinical benefit in CF, (iii) this can be achieved in a single formulation, and without the need for preconditioning, (iv) expression can last for 15 months, (v) readministration is feasible, (vi) the vector can transduce human air-liquid interface (ALI) cultures, and (vii) functional CF transmembrane conductance regulator (CFTR) chloride channels can be generated in vitro. Our data suggest that this lentiviral vector may provide a step change in airway transduction efficiency relevant to a clinical programme of gene therapy for CF.

Gene therapy for cystic fibrosis lung disease

Cystic fibrosis (CF) is characterised by respiratory and pancreatic deficiencies that stem from the loss of fully functional CFTR (CF transmembrane conductance regulator) at the membrane of epithelial cells. Current treatment modalities aim to delay the deterioration in lung function, Which is mostly responsible for the relatively short life expectancy of CF sufferers; however none have so far successfully dealt with the underlying molecular defect. Novel pharmacological approaches to ameliorate the lack of active CFTR in respiratory epithelial cells are beginning to address more of the pathophysiological defects caused by CFTR mutations. However, CFTR gene replacement by gene therapy remains the most likely option for addressing the basic defects, including ion transport and inflammatory functions of CFTR. In this chapter, We will review the latest preclinical and clinical advances in pharmacotherapy and gene therapy for CF lung disease.

Single-dose lentiviral gene transfer for lifetime airway gene expression

BACKGROUND

Cystic fibrosis (CF) is caused by a defect in cystic fibrosis transmembrane conductance regulator (CFTR) activity, often resulting in an incurable airway disease. Gene therapy into the conducting airway epithelium is a potential cure for CF; however, most gene vectors do not result in long-lived expression, and require re-dosing. Perversely, intrinsic host immune responses can then block renewed gene transfer.

METHODS

To investigate whether persistent gene expression could be achieved after a single dosing event, thus avoiding the issue of blocking host responses, we used a gene transfer protocol that combined an airway pretreatment using lysophosphatidylcholine with a human immunodeficiency virus type-1 (vesicular stomatitis virus G pseudotype) derived lentiviral vector to test whether an integrating vector could produce gene expression able to last for a substantial part of the lifetime of the laboratory mouse.

RESULTS

We found that a single dose of LV-LacZ produced immediate as well as lifetime mouse airway expression, confirming our hypothesis that use of an integrating vector extends transgene expression. Importantly, LV-CFTR dosing achieved at least 12 months of CFTR expression, representing partial functional correction of the CFTR defect in CF-null mice.

CONCLUSIONS

These findings validate the potential of this methodology for developing a gene transfer treatment for CF airway disease.

CpG-free plasmid DNA prevents deterioration of pulmonary function in mice

Nonviral gene vectors have been shown to be therapeutically effective in various animal models of inherited and acquired lung diseases. Although an acute unmethylated CG dinucleotide (CpG)-mediated inflammatory response has been previously observed for first-generation plasmids, its effect on pulmonary function has not been investigated to date. Here, we present data on lung functional parameters together with histopathology, cellular and inflammatory events in response to pulmonary administration of DNA-containing particles. We show that aerosol delivery of polyethylenimine gene vectors containing a first-generation CpG-rich plasmid induced an inflammatory response which was associated with a decrease in lung compliance. In contrast to these observations, aerosol application of CpG-free plasmid DNA prevented immune response and impairment of pulmonary function. These results demonstrate that aerosol delivery of CpG-free plasmid DNA is critical to avoid alteration of pulmonary function. Therefore, we suggest to use CpG-free pDNA for gene delivery to the lungs in future.

Modulation of expression of IL-8 gene in bronchial epithelial cells by 5-methoxypsoralen

Persistent recruitment of neutrophils in the bronchi of cystic fibrosis patients contributes to airway tissue damage, suggesting the importance of intervening on the expression of the neutrophil chemokine IL-8. Extracts from plants have been investigated to select components able to reduce IL-8 expression in bronchial epithelial cells challenged with Pseudomonas aeruginosa. Extracts and purified components have been added to cells 24 h before pro-inflammatory challenge with P. aeruginosa and IL-8 transcription was quantified in the IB3-1 CF cells in vitro. P. aeruginosa-dependent IL-8 mRNA induction was increased by Argemone mexicana and Vernonia anthelmintica whereas no significant modification of transcription was observed with Aphanamixis polystachya, Lagerstroemia speciosa and Hemidesmus indicus. Finally, inhibition of IL-8 was observed with Polyalthia longifolia (IC50=200 microg/ml) and Aegle marmelos (IC50=20 microg/ml). Compounds from A. marmelos were isolated and identified by GC-MS. No significant effect was observed with butyl-p-tolyl sulphate, whereas the inhibition obtained with 6-methyl-4-chromanone concentration was accompanied by an anti-proliferative effect. On the contrary, 5-methoxypsoralen resulted in IL-8 inhibition at 10 microM concentration, without effects on cell proliferation. In synthesis, 5-methoxypsoralen can be taken into consideration to investigate mechanisms of neutrophil chemotactic signalling and for its potential application in modulating the excessive CF lung inflammation.

Cystic fibrosis

Cystic fibrosis is the most common lethal genetic disease in white populations. The outlook for patients with the disease has improved steadily over many years, largely as a result of earlier diagnosis, more aggressive therapy, and provision of care in specialised centres. Researchers now have a more complete understanding of the molecular-biological defect that underlies cystic fibrosis, which is leading to new approaches to treatment. One of these treatments, hypertonic saline, is already in use, whereas others are in advanced stages of development. We review clinical care for cystic fibrosis and discuss recent advances in the understanding of its pathogenesis, implementation of screening of neonates, and development of therapies aimed at treating the basic defect.

Functional cystic fibrosis transmembrane conductance regulator expression in cystic fibrosis airway epithelial cells by AAV6.2-mediated segmental trans-splicing

Cystic fibrosis is characterized by deficiency of the cystic fibrosis transmembrane conductance regulator (CFTR), a Cl(-) transporter. The packaging constraints of adeno-associated viral (AAV) vectors preclude delivery of both an active promoter and CFTR cDNA to target cells. We hypothesized that segmental trans-splicing, in which two AAV vectors deliver the 5' and 3' halves of the CFTR cDNA, could mediate splicing of two pre-mRNAs into a full-length, functional CFTR mRNA. Using a segmental trans-splicing 5' donor-3' acceptor pair that split the CFTR cDNA between exons 14a and 14b, cotransfection of donor and acceptor plasmids into CFTR(-) cells resulted in full-length CFTR message and protein. Microinjection of plasmids into CFTR(-) cells produced cAMP-activated Cl(-) conductance. Vectors created with an engineered human serotype, AAV6.2, were used to deliver CFTR donor and acceptor constructs, resulting in full-length CFTR mRNA and protein as well as cAMP-activated Cl(-) conductance in CFTR(-) cells, including human CF airway epithelial IB3-1 cells. Thus, segmental trans-splicing can be used with AAV vectors to mediate expression of CFTR, a strategy potentially applicable to individuals with CF.

Extracellular barriers in respiratory gene therapy

Respiratory gene therapy has been considered for the treatment of a broad range of pulmonary disorders. However, respiratory secretions form an important barrier towards the pulmonary delivery of therapeutic nucleic acids. In this review we will start with a brief description of the biophysical properties of respiratory mucus and alveolar fluid. This must allow the reader to gain insights into the mechanisms by which respiratory secretions may impede the gene transfer efficiency of nucleic acid containing nanoparticles (NANs). Subsequently, we will summarize the efforts that have been done to understand the barrier properties of respiratory mucus and alveolar fluid towards the respiratory delivery of therapeutic nucleic acids. Finally, new and current strategies that can overcome the inhibitory effects of respiratory secretions are discussed.

Gene transfer to the lung: lessons learned from more than 2 decades of CF gene therapy

Gene therapy is currently being developed for a wide range of acute and chronic lung diseases. The target cells, and to a degree the extra and intra-cellular barriers, are disease-specific and over the past decade the gene therapy community has recognized that no one vector is good for all applications, but that the gene transfer agent (GTA) has to be carefully matched to the specific disease target. Gene therapy is particularly attractive for diseases that currently do not have satisfactory treatment options and probably easier for monogenic disorders than for complex diseases. Cystic fibrosis (CF) fulfils these criteria and is, therefore, a good candidate for gene therapy-based treatment. This review will focus on CF as an example for lung gene therapy, but lessons learned may be applicable to other target diseases.

Gene delivery into hepatocytes with the preS/liposome/DNA system

Gene delivery into human hepatocytes remains a critical issue for the development of liver-directed gene therapy. Gene delivery based on non-viral vectors is an attractive approach relative to viral vectors. In this report, novel delivery system of preS/liposome/DNA virus-like particle (VLP) was developed for gene transfection into hepatocytes in vivo and in vitro. Plasmid pCMVbeta, expressing beta-galactosidase, was encapsulated with cationic liposome, and then the histidine-tagged preS domain of hepatitis B virus was coated on the surface of liposome/DNA to form preS/liposome/ DNA VLP. Transfection efficiencies of preS/liposome/DNA, liposome/DNA, naked DNA and preS were analyzed using several different human cell lines. The highest transfection efficiency was found using preS/liposome/DNA VLP as the transfection reagent in human hepatocyte (HH) cell line. Results show that preS domain of hepatitis B virus coated on liposome/DNA can be used for highly efficient gene transfection into human hepatocytes. Moreover, the target characteristic of preS/liposome/DNA was analyzed in vivo. After preS/liposome/DNA VLP was injected into immunocompromised (Nude) mice via the tail vein, most of beta-galactosidase was expressed in the liver; however, no significant target expression was found with the injection of liposome/ DNA or naked DNA. Our results show that preS/liposome/DNA VLP can be used as a novel liver-specific gene delivery system.

Targeted delivery of nucleic-acid-based therapeutics to the pulmonary circulation

Targeted delivery of functional nucleic acids (genes and oligonucleotides) to pulmonary endothelium may become a novel therapy for the treatment of various types of lung diseases. It may also provide a new research tool to study the functions and regulation of novel genes in pulmonary endothelium. Its success is largely dependent on the development of a vehicle that is capable of efficient pulmonary delivery with minimal toxicity. This review summarizes the recent progress that has been made in our laboratory along these research directions. Factors that affect pulmonary nucleic acids delivery are also discussed.

Progress and prospects: the design and production of plasmid vectors

Plasmid DNA (pDNA) expression vectors are fundamental to all forms of non-viral gene transfer. In this review, we discuss principles of pDNA design and production including the impact of bacterially derived sequences on transgene expression and minicircle approaches to minimize their effects. The impact of inclusion of DNA elements such as scaffold matrix attachment regions (S/MARs), transcription factor (TF)-binding sites and tissue-specific promoters are described. The benefits of eliminating CG dinucleotides (CpGs) from the pDNA are also considered.

What's new in cystic fibrosis? From treating symptoms to correction of the basic defect

Chronic relentless lung infection and pancreatic insufficiency are the cardinal features of cystic fibrosis (CF), a life-shortening autosomal recessive disease. Mutations in the 'cystic fibrosis transmembrane conductance regulator' (CFTR) are currently classified into five groups according to their repercussion on CFTR protein synthesis and its chloride channel function. Stop codon mutations (class I) result in a truncated nonfunctional CFTR, class II mutations consist of aberrantly folded CFTR protein that is degraded by the cell quality control system, while class III mutations lead to defective regulation of the CFTR protein and, consequently, the absence of CFTR function. These three classes usually lead to a classic CF phenotype with pancreatic insufficiency. CFTR mutations that lead to defective chloride conductance are grouped together in class IV. Class V mutations interfere with normal transcription, thereby reducing the amount of otherwise normal CFTR. These latter two classes are mostly associated with a milder expression of the disease. In the absence of CFTR function, unrestrained Na+ absorption and the failure of active Cl- secretion lead to a decreased airway surface liquid (ASL) volume and subsequent failure of normal mucociliary clearance. This review highlights recent therapeutic strategies that either target the underlying defect or the early steps in CF pathophysiology. To date, gene therapy has failed to demonstrate a clinical benefit after repeated administration. Mutation-specific chloride channel correction pharmacotherapy is currently being developed, an example of which is PTC124, a new chemical compound that selectively induces read-through of premature stop codons. However, clinical efficacy for most of the compounds still has to be proven in large clinical trials. The positive effect of nebulised hypertonic saline on mucociliary clearance is based on the restoration of ASL height. Recent advances in the current treatment of lung infection and inflammation are highlighted in this review. Lung transplantation should be considered in terminally ill patients, but the timing of the transplantation is crucial: transplanting too early shortens survival, while transplanting too late results in patients dying on the waiting list.

Recent advances in cystic fibrosis

Considerable advances in cystic fibrosis (CF) research have translated into improved patient care, reflected by a continuing trend of improving life expectancy in CF patients. This review summarises some of the major findings of CF research that have occurred in the past year. The review specifically focuses on those developments that have direct implications for patient care or those in which clinical trials suggest benefits that may impact on the treatment of CF patients in the near future.

Bactofection of lung epithelial cells in vitro and in vivo using a genetically modified Escherichia coli

Bacteria-mediated gene transfer ('bactofection') has emerged as an alternative approach for genetic vaccination and gene therapy. Here, we assessed bactofection of airway epithelial cells in vitro and in vivo using an attenuated Escherichia coli genetically engineered to invade non-phagocytic cells. Invasive E. coli expressing green fluorescent protein (GFP) under the control of a prokaryotic promoter was efficiently taken up into the cytoplasm of cystic fibrosis tracheal epithelial (CFTE29o-) cells and led to dose-related reporter gene expression. In vivo experiments showed that following nasal instillation the vast majority of GFP-positive bacteria pooled in the alveoli. Further, bactofection was assessed in vivo. Mice receiving 5 x 10(8) E. coli carrying pCIKLux, in which luciferase (lux) expression is under control of the eukaryotic cytomegalovirus (CMV) promoter, showed a significant increase (P<0.01) in lux activity in lung homogenates compared to untransfected mice. Surprisingly, similar level of lux activity was observed for the non-invasive control strain indicating that the eukaryotic CMV promoter might be active in E. coli. Insertion of prokaryotic transcription termination sequences into pCIKLux significantly reduced prokaryotic expression from the CMV promoter allowing bactofection to be detected in vitro and in vivo. However, bacteria-mediated gene transfer leads to a significantly lower lux expression than cationic lipid GL67-mediated gene transfer. In conclusion, although proof-of-principle for lung bactofection has been demonstrated, levels were low and further modification to the bacterial vector, vector administration and the plasmids will be required.

Cystic fibrosis: a review of pulmonary and nutritional therapies

In summary, there is a significant interplay between the pulmonary manifestations and nutritional status of CF patients. The advances in CF clinical care in the past 2 decades are mainly attributed to anti-infective therapy as well as aggressive nutritional management. Currently, there are multiple therapeutic agents that are in clinical trial that target either the underlying CFTR defect or the downstream effects of CFTR. The broad spectrum of therapeutic agents being studied as well as the advances in therapies that target the underlying CFTR defect are exciting, making it likely that at least one of the treatments will make a major difference in how we will treat CF in the future.